1. Field of the Invention
The present invention relates to a bandwidth measuring method and apparatus for a packet switching network in which a plurality of test packets are fed to a packet switching network so that the bandwidth is measured, and more specifically relates to a bandwidth measuring method and apparatus for a packet switching network in which even a bandwidth (capacity) of a link that is distant from a tester that transmits test packets can be measured.
2. Description of the Related Art
FIG. 4 is a diagram showing a conventional bandwidth measuring method for a packet switching network. A receiver 40 is connected to a tester 10 via two transit nodes 20A, 20B.
In FIG. 4, the line width of each link 30A, 30B, 30C connecting among the tester 10, each transit nodes 20A, 20B and the receiver 40 represent the bandwidth of each one, respectively, and here, the bandwidth of the link 30B between the transit nodes 20A, 20B is narrower than those of other links 30A, 30C, thereby forming a so-called bottleneck.
A tester 10 as a bandwidth measuring apparatus feeds two (or more) test packets TPa, TPb, which have the same packet length L to a link 30A. When receiving each test packet, a transit node 20A transfers one after another each test packet TPa, TPb to a link 30B of its latter part, each time a reception is completed. The transit node 20A starts receiving the test packet TPa at the time t1, and competes the reception at the time (t1+xcex94t1) that is xcex94t1 after t1. Receiving the test packet TPb starts immediately after the completion of the reception of the test packet TPa, and the transit node 20A completes the reception at the time (t1+2xc2x7xcex94t1) that is xcex94t1 after the completion of the reception of the test packet TPa.
When the transit node 20A is a receiver, the difference (=xcex94t1) between the reception completion time of the test packet TPb (t1+2xc2x7xcex94t1) and the reception completion time of the test packet TPa (t1+xcex94t1) is calculated. This difference xcex94t1 corresponds to a transfer time of the test packet TPb by the link 30A as far as the reception completion timing of the test packet TPa at the transit node 20A (receiver) and the reception starting timing of the test packet TPb correspond to each other. The bandwidth of the link 30A can be determined at the transit node 20A (receiver) based on the difference xcex94t1 and the packet length L of the test packet TPb.
In FIG. 4, a transit node 20B receives the test packet TPa via the link 30B at the time t2, and when the transit node 20B completes the reception xcex94t2 after, it immediately transfers the test packet TPa received to a link 30C. Similarly, the transit node 20B completes the reception of the test packet TPb at the time (t2+2xc2x7xcex94t2) and immediately transfers it to the link 30C. Since the bandwidth of the link 30B is narrower than that of the link 20A, the period xcex94t2 that the transit node 20B requires to receive each test packet TPa, TPb becomes longer than the xcex94t1.
If the bandwidth of the link 30C that is the latter part is sufficiently wide as similar to the link 30A, as the transit node 20B starts transferring the test packet TPa at the time t3, the transfer can be completed after xcex94t3 ( less than xcex94t2) that is similar to the xcex94t1. However, since xcex94t3 is shorter than the xcex94t2, at the transit node 20B at the time (t3+xcex94t3), when the transfer of the TPa is completed, the reception of the test packet TPb is not completed. Thus, the transit node 20B cannot start transferring the test packet TPb immediately after the transferring of the test packet TPa is completed.
The transit node 20B, immediately after completing the reception of the test packet TPb at the time (t2+2xc2x7xcex94t2), transfers it to a receiver 40. However, after the completion of the reception of the first test packet TPa at the time t4, an empty time (between packets gap) xcex94t gap is generated at the receiver 40 until the reception of the next test packet TPb is started. When the reception of the test packet TPb is completed xcex94t4 after the start of the reception, the times when the receiver 40 completes the receptions of each test packet TPa, TPb become t4, (t4+xcex94t gap+xcex94t4), respectively. Since the difference (xcex94t gap+xcex94t4) extra includes the between packets gap xcex94t gap, a true transmitting time of the test packet TPb is not represented. Therefore, the receiver 40 cannot determine the bandwidth of the link 30C based on the difference (xcex94t gap+xcex94t4) and the packet length L of the test packet TPb.
The object of the present invention is to provide a bandwidth measuring method and apparatus for a packet switching network in which a bandwidth of a link that is distant from a tester that transmits test packets, specifically a bandwidth distant beyond a bottleneck, can be measured.
A feature of the present invention is to that, a bandwidth measuring method for a packet switching network in which a bandwidth of a packet switching network comprising a plurality of nodes for packet switching connected mutually is measured, said method comprising a procedure in which a plurality of test packets which at least include two test packets having different packet length are fed to the packet switching network so that in said two test packet, the test packet having a long packet length and the test packet having a short packet length are successive in this order, and a procedure in which a receiver receiving each test packet determines an immediately former bandwidth based on the difference in the reception completion timing thereof.
According to the aforementioned characteristics, in two test packets that were successively fed, since the packet length (L1) of the first test packet (TPI) is longer than the packet length (L2) of the next test packet (TP2). Therefore, the transit node to whose latter part a target link is connected can complete the receiving of the next test packet (TP2) from the link of the former part until feeding of the first received test packet (TP1) to the target link is completed, even when the bandwidth of the link that is connected to the former part of the transit node is narrower than that of the target link.
Therefore, to the target link of the latter part, the next test packet (TP2) can be fed at the same time when feeding of the first test packet (TP1) is completed, thereby enabling prevention of generation of a between packets gap of each test packet on the target link of the latter part. As a result of this, since the difference of the times when the receiver of the latter part completes receiving of each test packet represents the times that the target link requires to transfer the test packet (TP2), the receiver can determine the bandwidth of the target link based on the difference of the receiving completion times and the packet length of the test packet (TP2).